The field of the invention relates generally to inductor-inductor-capacitor (LLC) converters, and more specifically, to improving load transient response using an LLC converter.
Rectifiers that employ a front power factor correction (PFC) circuit and an LLC DC/DC converter adjust the PFC output voltage to increase efficiency of the whole converter system. Efficiency is increased in such systems by operating the LLC converter near its series resonant frequency. During an output load change, the LLC converter quickly adjusts the output voltage, causing its controller to saturate and reach minimum frequency, which is equivalent to reaching a maximum of 99% duty cycle in a PWM controller. Since the boost response is slow, the output voltage sags because the PFC output voltage droops.
Another known method of increasing efficiency typically involves employing a separate optocoupler circuit to transmit output load current information to a PFC controller to adjust the PFC output voltage during load transients or use a faster communication port to transfer data between primary and secondary digital signal processors (DSPs). Still another known method uses a current sense transformer on a primary side of the LLC converter. Such known methods typically require additional, costly components, which often lack the response time necessary for LLC converter operation.